1. Field of the Invention
The present invention relates to a process for producing a pyridine derivative having a trifluoromethyl group at .beta.-position thereof directly from .beta.-picoline. More particularly, it relates to a process for producing a pyridine derivative having a trifluoromethyl group at .beta.-position thereof by a vapor phase reaction of .beta.-picoline with chlorine and hydrogen fluoride, if necessary, in the presence of a catalyst of a specific metal fluoride.
2. Description of the Prior Arts
Pyridine derivatives having a trifluoromethyl group at .beta.-position thereof have been found to be converted into the important compounds having excellent physiological activities and have been considered as important intermediates for agricultural chemicals and medicines. 2-Chloro-5-trifluoromethylpyridine is especially the important intermediate for herbicides, insecticides and fungicides. Therefore, it has been required to find an industrial process for producing such compounds in a mass production and an economical manner.
Thus, it has not been found so many reports for productions of said pyridine derivatives since the utilities of said pyridine derivatives have not been considered to be important.
It has been described that a chlorination of methyl group of .beta.-picoline is difficult in a production of .beta.-trichloromethylpyridine which has the similar structure to said pyridine derivatives in HELVETICA CHIMICA ACTA vol. 59, Fase 1, Nr. 19-20, 1976, etc. Therefore, it has not been expected to produce said pyridine derivatives from .beta.-picoline.
Recently, it has been proposed to produce said pyridine derivatives in European Pat. Nos. 0000483 and WO79/00094 etc. In these prior arts, only experimental small scale processes are disclosed. For example, in WO 79/00094, it has been disclosed as a process for producing chloro .beta.-trifluoromethylpyridines, that (1) chlorine gas is fed into a solution of .beta.-picoline in carbon tetrachloride under ultraviolet radiation at 80.degree. C. for 3 hours to produce chloro .beta.-trichloromethylpyridines at an yield of less than 10%; (2) chloro .beta.-trifluoromethylpyridines are produced by reacting the chloro .beta.-trichloromethylpyridines with antimony trifluoride in a liquid phase at 140.degree. to 145.degree. C. for 1 hour or reacting the chloro .beta.-trichloromethylpyridines with hydrogen fluoride in a liquid phase at 200.degree. C. for 10 hours in an autoclave.
The process, however, has the following disadvantages.
(1) it takes a long time for the chlorination and the fluorination; PA0 (2) the chlorination is not smoothly performed to produce a large amount of by-products and to be lower yield and the operations for the purification and the separation are complicated; PA0 (3) anitmony trifluoride is expensive and causes a trouble in a treatment of a waste solution and an autoclave is required for the reaction with hydrogen fluoride.